I would have her checked out by a good bully vet. Sometimes when they are young the hip are a little loose and will tighten up with age, but it could also be dysplasia.
I agree with above advice, and the best thing to do is have her looked at by your vet, to have it checked out, and maybe an X-ray to get a better picture of what's going on with her hips. I hope it's nothing serious. Please keep us posted.